dvm_lock_sample 解析

最近中在看art代碼，看到這個函數的時候，想到logcat的events log中有大量的dvm_lock_sameple信息

進程名，主線程？，線程名字，鎖等待時間，當前持有者的文件名，行號，上一個持有者文件名，行號，鎖等待的百分比

1. 打印此條LOG的時候，上一個鎖的持有者已經釋放鎖，本線程爲下一個鎖的持有者，即將獲取鎖
2. 上一個持有者的文件名，可能是“-”，表示與持有者是同一個文件。

dvm_lock_sample: [com.banyac.midrive.launcher,1,main,6,SourceFile,234,-,358,1]

• 1

art/runtime/monitor_android.cc

void Monitor::LogContentionEvent(Thread* self, uint32_t wait_ms, uint32_t sample_percent,
                                 const char* owner_filename, uint32_t owner_line_number) {
  // Emit the event list length, 1 byte.
  char eventBuffer[174];
  char* cp = eventBuffer;
  *cp++ = 9;

  // Emit the process name, <= 37 bytes.
  int fd = open("/proc/self/cmdline", O_RDONLY);
  char procName[33];
  memset(procName, 0, sizeof(procName));
  read(fd, procName, sizeof(procName) - 1);
  close(fd);
  size_t len = strlen(procName);
  cp = EventLogWriteString(cp, procName, len);

  // Emit the sensitive thread ("main thread") status, 5 bytes.
  cp = EventLogWriteInt(cp, Monitor::IsSensitiveThread());

  // Emit self thread name string, <= 37 bytes.
  std::string thread_name;
  self->GetThreadName(thread_name);
  cp = EventLogWriteString(cp, thread_name.c_str(), thread_name.size());

  // Emit the wait time, 5 bytes.
  cp = EventLogWriteInt(cp, wait_ms);

  // Emit the source code file name, <= 37 bytes.
  uint32_t pc;
  mirror::ArtMethod* m = self->GetCurrentMethod(&pc);
  const char* filename;
  uint32_t line_number;
  TranslateLocation(m, pc, &filename, &line_number);
  cp = EventLogWriteString(cp, filename, strlen(filename));

  // Emit the source code line number, 5 bytes.
  cp = EventLogWriteInt(cp, line_number);

  // Emit the lock owner source code file name, <= 37 bytes.
  if (owner_filename == NULL) {
    owner_filename = "";
  } else if (strcmp(filename, owner_filename) == 0) {
    // Common case, so save on log space.
    owner_filename = "-";
  }
  cp = EventLogWriteString(cp, owner_filename, strlen(owner_filename));

  // Emit the source code line number, 5 bytes.
  cp = EventLogWriteInt(cp, owner_line_number);

  // Emit the sample percentage, 5 bytes.
  cp = EventLogWriteInt(cp, sample_percent);

  CHECK_LE((size_t)(cp - eventBuffer), sizeof(eventBuffer));
  android_btWriteLog(EVENT_LOG_TAG_dvm_lock_sample, EVENT_TYPE_LIST, eventBuffer,
                     (size_t)(cp - eventBuffer));
}